I was just wondering, why did need to stir th cryo tanks on the Apollo missions??Andrew

Because LOX stratifies in 0g and to get an accurate measurement of the amount remaining, it needed to be stirred to make it homogenous

Very interesting. Can you provide a link to give more details on the nature of the statification and how quantity was measured? I am very familiar with quantity measurement in shuttle RCS and OMS and it involves using the pressure and temperate of the helium. This obviously wouldn't work for LOX tanks.

Let's make this into an Apollo Program Q&A thread.I'd like to know how the Atmosphere in teh Command module was composed and at what pressure it was mantained. I'd also like to know if it was different then what is used on Soyuz how this was handled during ATSP

Let's make this into an Apollo Program Q&A thread.I'd like to know how the Atmosphere in teh Command module was composed and at what pressure it was mantained. I'd also like to know if it was different then what is used on Soyuz how this was handled during ATSP

5 psia pure O2. Soyuz used (and still uses) 14.7 psia air. The ASTP docking module acted as an airlock between the two.

How came they adopted the idea of pure O2, that also lead to the Apollo 1 disaster? From a layman point of view it is so absurd. Carrying people in an Atmosphere alike the natural one on earth seems to be the only logical way to do it, but hey must have had reasons, what were they?My guess would be that with such an atmosphere you need less (no?) prebreath time when doing an EVA.

My guess would be that with such an atmosphere you need less (no?) prebreath time when doing an EVA.

Yes. It was used in orbit also after Apollo 1 but no longer while on the ground.

My understanding of the Apollo 1 accident report http://history.nasa.gov/Apollo204/content.html is that it has more to do with pressure, materials used etc. rather than Oxygen. The life support system kept feeding additional Oxygen to compensate for what the fire ate away. The internal pressure was rising and as a consequence the inward opening hatch could not be operated any more ...

I'm pretty sure a pure oxygen environment poses much higher risks for fire whatever you do. One example for this is that NASA ruled out the use of pencils on Apollo because they were deemed too flamable. This shouldn't be a problem in either Soyuz or on the ISS.

How came they adopted the idea of pure O2, that also lead to the Apollo 1 disaster? From a layman point of view it is so absurd. Carrying people in an Atmosphere alike the natural one on earth seems to be the only logical way to do it, but hey must have had reasons, what were they?My guess would be that with such an atmosphere you need less (no?) prebreath time when doing an EVA.

Main consideration was that pure O2 allows much lower pressure, which means the pressure vessel doesn't have to be as strong (and can be much lighter). This was critical to get the performance for lunar missions, especially the LM.

How came they adopted the idea of pure O2, that also lead to the Apollo 1 disaster? From a layman point of view it is so absurd. Carrying people in an Atmosphere alike the natural one on earth seems to be the only logical way to do it, but hey must have had reasons, what were they?My guess would be that with such an atmosphere you need less (no?) prebreath time when doing an EVA.

I am very familiar with quantity measurement in shuttle RCS and OMS and it involves using the pressure and temperate of the helium.

Those are standard diaphragm tanks that keep the prop and helium separate, right? Who makes them?

They have no diaphragms because diaphragms tend to fatigue and crack with multiple uses. They have screens that use fluid capillary tension to prevent the helium from leaving the tank and getting to the jets/engines. The OMS tanks also rely on acceleration from the OMS engines to keep the prop to the back during a OMS burn.

How came they adopted the idea of pure O2, that also lead to the Apollo 1 disaster? From a layman point of view it is so absurd.

Weight reduction.

I was waiting for an expert to answer and who might have some numbers on how much it saves in terms of launch mass. Anyway, for each kg of command module returning to Earth it took more than 500 kg of Saturn V launch mass! So, reducing the mass of this module really made the difference.

The atmosphere at sea level corresponds to a water column 10m/30ft tall. On the launch pad that is no issue given that internal and external pressure are in equilibrium. In space there is no outside pressure and so by taking out the nitrogen the internal pressure goes down to about one third. Hence less load on the structure.

BTW, this is also done in commercial airliners by lowering the cabin pressure when climbing to cruising altitude - although without changing the oxygen/nitrogen ratio. That means less O2 for the passengers than on sea level which is acceptable for sitting in a chair but not desirable when performing work in space for extended periods of time.

Mine may be a little of a bad question but I have always wondered. How did the Apollo crews access the SM? They had their seats behind them and under them they had the solid heat shield. Also how did they access the LM? They had the panels in front of them. Diagrams and pictures would be very helpful.